As the integration of ICs increases, exposure wavelengths become shorter in lithography. This is because the resolution in the optical exposure generally improves as the exposure wavelengths become short. Recently, the exposure wavelengths have been shortened from a KrF laser of 248 nm to an ArF laser of 193 nm. As the exposure wavelengths in the next-generation lithography, a remarkably shortened wavelength between 12 nm and 15 nm using extreme ultraviolet (hereinafter referred to as EUV) light is promising, rather than 157 nm wavelength using the F2 laser which is originally-promised.
At a wavelength of EUV light, the refraction index for every material is approximately 1, and light is absorbed. Thus, an optical lithographic system cannot be formed of lens and the like previously used, and required to be formed entirely of mirror optical systems. Needless to say, it is necessary that the transmission-type masks previously used as an exposure mask unexceptionally be changed to the reflective type.
For example, a structure including a reflecting layer which is provided on the substrate and reflects EUV light, and an absorbent layer which absorbs EUV light on the reflecting layer is adopted for the mask for EUV exposure. The IC pattern is formed by patterning the absorbent layer on the reflecting layer. Thus, unlike the binary mask or half-tone mask, in the mask for EUV exposure, the reflectance of light for exposure is higher in a part where the patterned film does not exist than in a part where there is patterned film.
The wavelength of the ultraviolet for use in the inspection for a mask for EUV exposure is preferably between 150 nm and 300 nm like the wavelength previously used, from the point of view of continuity of inspecting techniques and unnecessary introduction of a new inspecting apparatus. However, in the mask having optimum reflection characteristics with respect only to EUV light, there is a high chance that no sufficient contrast exists in the ultraviolet inspection light that has different wavelengths. Thus, proposed is a method for increasing the contrast at the inspection and improving the inspection performance for the mask, by providing an antireflection layer with respect to ultraviolet above the absorbent layer (as described, for example, in JP-A 2006-228767 (KOKAI)).